1. Field of the Invention
The present invention relates to a radio frequency amplifier module and, more particularly, to a radio frequency amplifier module integrated with a power control loop, which is relatively small in size and relatively low in parasitic impedance.
2. Description of the Related Art
Typically, radio frequency (RF) power amplifiers employed in transmitters of mobile terminals are classified into three groups: (1) discrete transistor line-ups, (2) monolithic microwave integrated circuits (MMICs), and (3) RF power amplifier modules. Of these three groups, the discrete transistor line-ups have been employed earliest, which have two primary disadvantages: (1) mobile phone manufacturers must design appropriate RF power amplifiers himself and (2) print circuit boards to be used must provide a relatively large area. These disadvantages result in a longer period of time for the RF power amplifiers to become available in commercial and industrial markets. In addition, design flexibility associated with the RF power amplifiers suffers from a number of parasitic impedances in the discrete transistor line-ups. Possible influences caused by the parasitic impedances become more complicated especially when an operation frequency gets higher, such as 1 GHz and more.
As a countermeasure to the problem regarding the parasitic impedances of the discrete transistor line-ups, the MMIC RF power amplifiers have been developed. The MMIC RF power amplifiers have smaller parasitic impedances as compared with the discrete transistor line-ups. However, sometimes in order to compromise processing variations and to reduce cost, some matching circuits such as output matching circuits are not directly integrated into the MMIC chips. This is referred to as partially matched MMICs. In this case, the uncompleted portion of the matching circuit is left behind as a task of mobile phone manufacturers to deal with.
In recent years, the power amplifier modules are widely applied to the transmitters of the mobile terminals. A main advantage of the power amplifier modules is a possibility to combine various technologies such as band selection switches and power control loops, thereby enhancing their own performance so as to meet requirements of future broadband systems such as code division multiple access (CDMA).
FIG. 1 is a schematic diagram showing a transmitter of a GSM mobile terminal provided with a conventional RF power amplifier module and a conventional power control loop. Referring to FIG. 1, in addition to a conventional RF power amplifier module 10, a transmitter of a GSM mobile terminal includes a power control loop consisting of two ceramic directional couplers 22 and 26, two attenuators 24 and 28, three power detectors 32, 34, and 36, and a power control application specific integrated circuit (ASIC) 60. The conventional RF power amplifier module 10 is formed with two RF power amplifiers 12 and 14, which are applied to different frequency bands, respectively.
More specifically, a radio frequency signal RF is input to an appropriate one of the RF power amplifiers 12 and 14 of the conventional RF power amplifier module 10 and then is radiated out from an antenna 50 through a power combiner 40. The RF power radiated from the antenna 50 has a level which is determined by a distance between a base station and a mobile terminal. Once the output level is selected, a control signal CS is sent out from a base band side for controlling the level of the RF power. However, in order to comply with regulations of the Federal Communications Commission (FCC), it is necessary to use the power control loop for accurately controlling the level of the RF power as will be described later.
In the power control loop shown in FIG. 1, the ceramic directional couplers 22 and 26 retrieve parts of the output power from the conventional RF power amplifier module 10 as power representation signals for indicating the level of the output power and then sends the power representation signals to the power detectors 32 and 34 through the attenuators 24 and 28, respectively. The attenuators 24 and 28 are optional and are used for adjusting the power representation signals. With the power detectors 32 and 34, the power representation signals are interpreted as voltage level signals. These voltage level signals are applied to the power control ASIC 60. Moreover, in order to eliminate influence caused by temperature variations on the power detectors 32 and 34, the power detector 36 is additionally connected between the power control ASIC 60 and ground for inputting a reference signal to the power control ASIC 60. The power control ASIC 60 compares the control signal CS from the base band side, the power representation signals from the power detectors 32 and 34, and the reference signal from the power detector 36, and then outputs power adjustment signals to the RF power amplifiers 12 and 14 of the RF power amplifier module 10 so as to adjust bias conditions of the RF power amplifiers 12 and 14 for obtaining desired power levels.
Since the conventional RF power amplifier 10 and each of the components of the power control loop have their own packages and are separate devices from each other, the transmitter of the conventional mobile terminal is relatively large in size and fails to meet a demand of size reduction. Moreover, because many wirings are used for interconnections between the discrete packages, the parasitic impedances such as wiring inductances and capacitances under bonding pads are inevitably generated, resulting in deteriorations of the operation speed and reliability of the conventional mobile terminal.
In view of the above-mentioned problem, an object of the present invention is to provide an RF power amplifier module, in which a power control loop is integrated, thereby achieving a relatively small size and minimum parasitic impedance.
According to one aspect of the present invention, an RF power amplifier module, which is formed on a print circuit board and packaged within a mold, includes: at least one RF power amplifier formed on a first semiconductor substrate for outputting a power signal; at least one matching circuit connected to the at least one RF power amplifier for output matching; at least one capacitor connected to the at least one matching circuit for retrieving part of the power signal as a power representation signal; at least one power detector formed on the first semiconductor substrate and connected to the at least one capacitor for interpreting the power representation signal as a voltage level signal; and a power control application specific integrated circuit (ASIC) formed on a second semiconductor substrate for receiving a power control signal from outside and the voltage level signal and outputting a power adjustment signal to the at least one RF power amplifier based on a result of comparison between the power control signal and the voltage level signal, wherein the at least one RF power amplifier, the at least one power detector, and the power control ASIC are mounted on the print circuit board in forms of bare dies.
In order to minimize the whole size, the RF power amplifier module according to the present invention employs the capacitor with a relatively small size in place of the prior art ceramic directional coupler. In addition to the capacitor, the RF power amplifier, the matching circuit, the power detector, and the power control ASIC are all integrated on the print circuit board without individual, discrete packages. Furthermore, the RF power amplifier and the power detector may be formed on a common semiconductor substrate. Therefore, the RF power amplifier module according to the present invention is integrated with the power control loop and has advantages of a small size and minimum parasitic impedance.